Wireless re-charge of an implantable medical device

ABSTRACT

Near-field energy transmitters for charging a rechargeable power source of an implantable medical device (IMD). In some cases, the transmitter may include an output driver that may drive a transmit coil such that near-field energy is transmitted to the IMD at a determined frequency. In some cases, the IMD may include a receiving coil that may capture the near-field energy and then convert the near-field energy into electrical energy that may be used to recharge the rechargeable power source. Since the rechargeable power source does not have to maintain sufficient energy stores in a single charge for the entire expected life of the IMD, the power source itself and thus the IMD may be made smaller while still meeting device longevity requirements.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/424,918 filed on Nov. 21, 2016, the disclosureof which is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates generally to implantable medical devices, andmore particularly to implantable medical devices that have a powersource that may be wirelessly recharged from a remote location such asfrom outside of the body.

BACKGROUND

Implantable medical devices are commonly used to perform a variety offunctions, such as to monitor one or more conditions and/or deliverytherapy to a patient. In some cases, an implantable medical device maydeliver neurostimulation therapy to a patient. In some cases, animplantable medical device may simply monitor one or more conditions,such as pressure, acceleration, cardiac events, and may communicate thedetected conditions or events to another device, such as anotherimplantable medical device or an external programmer.

In some cases, an implantable medical device may be configured todeliver pacing and/or defibrillation therapy to a patient. Suchimplantable medical devices may treat patients suffering from variousheart conditions that may result in a reduced ability of the heart todeliver sufficient amounts of blood to a patient's body. In some cases,heart conditions may lead to rapid, irregular, and/or inefficient heartcontractions. To help alleviate some of these conditions, variousdevices (e.g., pacemakers, defibrillators, etc.) may be implanted into apatient's body. When so provided, such devices can monitor and providetherapy, such as electrical stimulation therapy, to the patient's heartto help the heart operate in a more normal, efficient and/or safemanner. In some cases, a patient may have multiple implanted devicesthat cooperate to monitor and/or provide therapy to the patient's heart.

Some implantable medical devices must be relatively small because ofanatomical constraints. For example, leadless cardiac pacemakers areoften placed within a heart chamber. Due to their relatively small size,and because of their long life expectancy, a large fraction of theinternal space of such implantable medical devices is often consumed bya battery or other power source. As the battery life determines theuseful life expectancy of the implantable medical device, there is adesire to make the batteries as large as possible within the confines ofthe available space.

What would be desirable is an implantable medical device that hasrecharge capability for recharging a rechargeable power source of theimplantable medical device. This may give the implantable medical devicea longer useful life expectancy and/or may not require as much batteryspace permitting a significantly smaller device size. A smaller devicesize may make the device more easily deliverable and implantable in thebody, allow the device to be implantable in smaller and more confinedspaces in the body, and/or may make the device less expensive toproduce.

SUMMARY

The disclosure is directed to charging/recharging a power source of animplantable medical devices. While a leadless cardiac pacemaker is usedas an example implantable medical device, it should be understood thatthe disclosure can be applied to any suitable implantable medical deviceincluding, for example, neuro-stimulators, diagnostic devices includingthose that do not deliver therapy, and/or any other suitable implantablemedical device as desired.

In some cases, the disclosure pertains to a near-field energytransmitter for charging an implantable medical devices (IMD) such asleadless cardiac pacemakers (LCP) that include a rechargeable powersource such as a rechargeable battery, a rechargeable capacitor or arechargeable supercapacitor. In some cases, the transmitter may includean output drive that may drive a transmit coil such that the near-fieldenergy is transmitted to the IMD at a determined frequency andamplitude. In some cases, the IMD may include a receiving coil that maycapture the near-field energy and then convert the near-field energyinto electrical energy that may be used to recharge the rechargeablepower source. Accordingly, since the rechargeable power source does nothave to maintain sufficient energy stores in a single charge for theentire expected lifetime of the IMD, the power source itself and thusthe IMD may be made smaller while still meeting device longevityrequirements.

In an example of the disclosure, a near-field energy transmitter forcharging an IMD may include a transmit coil configured to transmitnear-field energy to the IMD. An output driver may be configured fordriving the transmit coil so that the transmit coil may transmit thenear-field energy at a transmit frequency, wherein the transmitfrequency may be adjustable. A monitor may be operatively coupled to theoutput driver and may detect a transmit power of the transmittednear-field energy. A controller may be operatively coupled to the outputdriver and the monitor and the controller may be configured to cause theoutput driver to adjust the transmit frequency of the near-field energyacross two or more transmit frequencies, identify the transmit power ofthe near-field energy at each of the two or more transmit frequenciesusing the monitor, select the transmit frequency of the two or moretransmit frequencies that results in a transmit power that has apredetermined characteristic, and set the transmit frequency of theoutput driver to the selected transmit frequency.

Alternatively or additionally to any of the embodiments above, thepredetermined characteristic of the transmit power may be that thetransmit power is the maximum transmit power identified for the two ormore transmit frequencies.

Alternatively or additionally to any of the embodiments above, at leastone of the transmit frequencies is a resonant frequency of the outputdriver and transmit coil, and the output driver includes an adjustableimpedance that is adjustable to produce the resonance frequency.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to detect a decrease in the transmit powerat the selected transmit frequency, and in response may cause the outputdriver to adjust the transmit frequency of the near-field energy acrosstwo or more transmit frequencies, identify the transmit power of thenear-field energy at each of the two or more transmit frequencies,select the transmit frequency of the two or more transmit frequenciesthat results in a transmit power that has a predeterminedcharacteristic, and set the transmit frequency of the output driver tothe selected transmit frequency.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to repeat from time to time the following:cause the output driver to adjust the transmit frequency of thenear-field energy across two or more transmit frequencies, identify thetransmit power of the near-field energy at each of the two or moretransmit frequencies, select the transmit frequency of the two or moretransmit frequencies that results in a transmit power that has apredetermined characteristic, and set the transmit frequency of theoutput driver to the selected transmit frequency.

Alternatively or additionally to any of the embodiments above, thenear-field energy transmitter may further include a posture sensor fordetecting a posture of a patient in which the implantable medical deviceis implanted, and wherein the controller may be configured to identify atransmit frequency for each of two or more postures by using the posturesensor to detect when the patient is in one of the two or more postures,and when in the detected posture, cause the output driver to adjust thetransmit frequency of the near-field energy across two or more transmitfrequencies, identify the transmit power of the near-field energy ateach of the two or more transmit frequencies using the monitor, selectthe transmit frequency of the two or more transmit frequencies thatresults in a transmit power that has a predetermined characteristic, andassociate the detected posture with the selected transmit frequency.

Alternatively or additionally to any of the embodiments above, thecontroller may be further configured to subsequently detect when thepatient is in one of the two or more postures, and in response, set thetransmit frequency of the output driver to the transmit frequency thatis associated with the detected posture.

Alternatively or additionally to any of the embodiments above, thenear-field energy transmitter may further include a communication blockfor communicating with the implantable medical device, and wherein thecommunication block may be configured to receive one or more messagesfrom the implantable medical device regarding the transmit power that isreceived by the implantable medical device.

Alternatively or additionally to any of the embodiments above, theoutput driver may be configured to drive the transmit coil so that thetransmit coil transmits the near-field energy at a transmit amplitude,wherein the transmit amplitude may be adjustable, and the controller maybe configured to adjust the transmit amplitude of the near-field energyso that the transmit power that is received by the implantable medicaldevice meets a predetermined characteristic, condition or criteria.

Alternatively or additionally to any of the embodiments above, thetransmit coil may comprise a plurality of transmit coils and the outputdriver may be configured to drive the plurality of transmit coils sothat the plurality of transmit coils may transmit the near-field energyalong a transmit vector, wherein the transmit vector may be adjustable,and the controller may be configured to adjust the transmit vector ofthe near-field energy so that the transmit power that is received by theIMD may meet a predetermined criteria.

Alternatively or additionally to any of the embodiments above, the oneor more messages received from the implantable medical device mayindicate whether the transmit power that is received by the implantablemedical device meets the predetermined characteristic, condition orcriteria.

Alternatively or additionally to any of the embodiments above, the oneor more messages received from the implantable medical device mayindicate whether the transmit power that is received by the implantablemedical device does not meet the predetermined characteristic, conditionor criteria.

Alternatively or additionally to any of the embodiments above, thenear-field energy transmitter may further include a flexible substrateconfigured to conform to a patient and house the transmitter coil.

Alternatively or additionally to any of the embodiments above, theflexible substrate may include a strap for securing the flexiblesubstrate in place, and wherein the flexible substrate may have targetfiducials to indicate a torso position of the patient relative to thetransmit coil.

Alternatively or additionally to any of the embodiments above, thenear-field energy transmitter may further include a ferromagnetic shieldalong a side of the transmit coil that may face away from theimplantable medical device during use.

Alternatively or additionally to any of the embodiments above, theflexible substrate may be configured to be worn by the patient.

Alternatively or additionally to any of the embodiments above, thenear-field energy transmitter may further include a second transmit coilhoused by the flexible substrate, wherein the transmit coil may beconfigured to be located on a front of the patient and the secondtransmit coil may be configured to be located on a side or back of thepatient.

Alternatively or additionally to any of the embodiments above, thecontroller may be further configured to issue a human perceptible alertif the transmit coil is deemed to be misaligned with the implantablemedical device.

In another example of the disclosure, a near-field energy transmitterfor charging an implantable medical device (IMD) may include a transmitcoil that may be configured to transmit near-field energy to theimplantable medical device. An output driver for driving the transmitcoil may be provided. The output driver may cause the transmit coil totransmit the near-field energy at a transmit frequency and a transmitamplitude, wherein at least one of the transmit frequency and transmitamplitude may be adjustable. A communication block may be included forcommunicating with the implantable medical device. The communicationblock may be configured to receive one or more messages from theimplantable medical device regarding the transmit power that is receivedby the implantable medical device. A controller may be operativelycoupled to the output driver and the communication block. The controllermay be configured to adjust one or more of the transmit frequency andtransmit amplitude of the near-field energy so that the transmit powerthat is received by the implantable medical device may meet apredetermined characteristic, condition or criteria.

Alternatively or additionally to any of the embodiments above, the oneor more messages received from the implantable medical device mayindicate whether the transmit power that is received by the implantablemedical device meets the predetermined characteristic, condition orcriteria, and/or whether the transmit power that is received by theimplantable medical device does and/or does not meet the predeterminedcharacteristic, condition or criteria.

In another example of the disclosure, a near-field energy transmitterfor chagrining an implantable medical device (IMD) may include one ormore transmit coils that may be configured to transmit near-field energyto the IMD. An output driver that may drive the one or more transmitcoils so that the one or more transmit coils may transmit the near-fieldenergy at a transmit frequency, a transmit vector and a transmitamplitude, wherein at least one of the transmit frequency, transmitvector and transmit amplitude is adjustable, a communication block thatmay communicate with the IMD, wherein the communication block may beconfigured to receive one or more messages from the IMD regarding thetransmit power that is received by the IMD, and a controller that may beoperatively coupled to the output driver and the communication block,the controller may be configured to adjust one or more of the transmitfrequency, the transmit vector and the transmit amplitude of thenear-field energy so that the transmit power that is received by the IMDmay meet a predetermined criteria.

In another example of the disclosure, an implantable medical device(IMD) may be configured to be implanted within a patient's body and mayinclude a housing that may be configured for trans-catheter deployment.A plurality of electrodes that may be exposed external to the housing.Therapeutic circuitry that may be disposed within the housing and may beoperatively coupled to the plurality of electrodes and may be configuredto sense one or more signals via one or more of the plurality ofelectrodes and/or to stimulate tissue via one or more of the pluralityof electrodes. A rechargeable power source may be disposed within thehousing and may be configured to power the therapeutic circuitry. Areceiving coil may be configured to receive non-radiative near-fieldenergy through the patient's body. Charging circuitry may be operativelycoupled with the receiving coil and the rechargeable power source andmay be configured to use the non-radiative near-field energy receivedvia the receiving coil to charge the rechargeable power source. Acontroller may be disposed within the housing and may be configured todetect whether the non-radiative near-field energy received by thereceiving coil meets a predetermined characteristic, condition orcriteria and communicate a message to a remotely located near-fieldenergy transmitter indicating if the non-radiative near-field energyreceived by the receiving coil meets and/or does not meet thepredetermined characteristic, condition or criteria.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure may be more completely understood in consideration of thefollowing description in connection with the accompanying drawings, inwhich:

FIG. 1 is a schematic block diagram of an illustrative LCP in accordancewith an example of the disclosure;

FIG. 2 is a schematic block diagram of another illustrative medicaldevice that may be used in conjunction with the LCP of FIG. 1;

FIG. 3 is a schematic diagram of an exemplary medical system thatincludes multiple LCPs and/or other devices in communication with oneanother;

FIG. 4 is a schematic diagram of a system including an LCP and anothermedical device, in accordance with an example of the disclosure;

FIG. 5 is a side view of an illustrative implantable leadless cardiacdevice;

FIG. 6 is a schematic diagram of a patient with a rechargeableimplantable medical device system;

FIG. 7 is a schematic of an illustrative circuit for a coupled inductorsystem;

FIG. 8 is a schematic diagram of an illustrative implantable medicaldevice (IMD) according to an example of the disclosure;

FIG. 9 is a schematic diagram of an illustrative transmitter accordingto an example of the disclosure;

FIG. 10 is a schematic diagram of another illustrative transmitteraccording to an example of the disclosure;

FIG. 11 is a schematic diagram of another illustrative transmitteraccording to an example of the disclosure;

FIG. 12 is a schematic diagram of another illustrative transmitteraccording to an example of the disclosure;

FIG. 13A provides a side-view of an illustration of a coil configurationfor a near-field transmitter containing multiple transmit coils;

FIG. 13B provides a front-view of the illustration of the coilconfiguration for a near-field transmitter containing multiple transmitcoils;

FIG. 14A is an illustrative flexible substrate that may house a transmitcoil according to an example of the disclosure;

FIG. 14B is an illustrative flexible substrate, placed on a chair, thatmay house a transmit coil according to an example of the disclosure;

FIG. 14C is an illustrative flexible substrate, worn by a patient, thatmay house a transmit coil according to an example of the disclosure;

FIG. 15A is another illustrative flexible substrate that may house twotransmit coils according to an example of the disclosure; and

FIG. 15B is an illustrative flexible substrate, worn by a patient, thatmay house two transmit coils according to an example of the disclosure.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the disclosureto the particular embodiments described. On the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the spirit and scope of the disclosure.

DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about,” whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”,“some embodiments”, “other embodiments”, etc., indicate that theembodiment described may include one or more particular features,structures, and/or characteristics. However, such recitations do notnecessarily mean that all embodiments include the particular features,structures, and/or characteristics. Additionally, when particularfeatures, structures, and/or characteristics are described in connectionwith one embodiment, it should be understood that such features,structures, and/or characteristics may also be used connection withother embodiments whether or not explicitly described unless clearlystated to the contrary.

The following description should be read with reference to the drawingsin which similar structures in different drawings are numbered the same.The drawings, which are not necessarily to scale, depict illustrativeembodiments and are not intended to limit the scope of the disclosure.While a leadless cardiac pacemaker is used as an example implantablemedical device, it should be understood that the disclosure can beapplied to any suitable implantable medical device including, forexample, neuro-stimulators, diagnostic devices including those that donot deliver therapy, and/or any other suitable implantable medicaldevice as desired.

FIG. 1 depicts an illustrative leadless cardiac pacemaker (LCP) that maybe implanted into a patient and may operate to deliver appropriatetherapy to the heart, such as to deliver anti-tachycardia pacing (ATP)therapy, cardiac resynchronization therapy (CRT), bradycardia therapy,and/or the like. As can be seen in FIG. 1, the LCP 100 may be a compactdevice with all components housed within the or directly on a housing120. In some cases, the LCP 100 may be considered as being an example ofan implantable medical device (IMD). In the example shown in FIG. 1, theLCP 100 may include a communication module 102, a pulse generator module104, an electrical sensing module 106, a mechanical sensing module 108,a processing module 110, a battery 112, and an electrode arrangement114. The LCP 100 may include more or less modules, depending on theapplication.

The communication module 102 may be configured to communicate withdevices such as sensors, other medical devices such as an SICD, and/orthe like, that are located externally to the LCP 100. Such devices maybe located either external or internal to the patient's body.Irrespective of the location, external devices (i.e. external to the LCP100 but not necessarily external to the patient's body) can communicatewith the LCP 100 via communication module 102 to accomplish one or moredesired functions. For example, the LCP 100 may communicate information,such as sensed electrical signals, data, instructions, messages, R-wavedetection markers, etc., to an external medical device (e.g. SICD and/orprogrammer) through the communication module 102. The external medicaldevice may use the communicated signals, data, instructions, messages,R-wave detection markers, etc., to perform various functions, such asdetermining occurrences of arrhythmias, delivering electricalstimulation therapy, storing received data, and/or performing any othersuitable function. The LCP 100 may additionally receive information suchas signals, data, instructions and/or messages from the external medicaldevice through the communication module 102, and the LCP 100 may use thereceived signals, data, instructions and/or messages to perform variousfunctions, such as determining occurrences of arrhythmias, deliveringelectrical stimulation therapy, storing received data, and/or performingany other suitable function. The communication module 102 may beconfigured to use one or more methods for communicating with externaldevices. For example, the communication module 102 may communicate viaradiofrequency (RF) signals, inductive coupling, optical signals,acoustic signals, conducted communication signals, and/or any othersignals suitable for communication.

In the example shown in FIG. 1, the pulse generator module 104 may beelectrically connected to the electrodes 114. In some examples, the LCP100 may additionally include electrodes 114′. In such examples, thepulse generator 104 may also be electrically connected to the electrodes114′. The pulse generator module 104 may be configured to generateelectrical stimulation signals. For example, the pulse generator module104 may generate and deliver electrical stimulation signals by usingenergy stored in the battery 112 within the LCP 100 and deliver thegenerated electrical stimulation signals via the electrodes 114 and/or114′. Alternatively, or additionally, the pulse generator 104 mayinclude one or more capacitors, and the pulse generator 104 may chargethe one or more capacitors by drawing energy from the battery 112. Thepulse generator 104 may then use the energy of the one or morecapacitors to deliver the generated electrical stimulation signals viathe electrodes 114 and/or 114′. In at least some examples, the pulsegenerator 104 of the LCP 100 may include switching circuitry toselectively connect one or more of the electrodes 114 and/or 114′ to thepulse generator 104 in order to select which of the electrodes 114/114′(and/or other electrodes) the pulse generator 104 delivers theelectrical stimulation therapy. The pulse generator module 104 maygenerate and deliver electrical stimulation signals with particularfeatures or in particular sequences in order to provide one or multipleof a number of different stimulation therapies. For example, the pulsegenerator module 104 may be configured to generate electricalstimulation signals to provide electrical stimulation therapy to combatbradycardia, tachycardia, cardiac synchronization, bradycardiaarrhythmias, tachycardia arrhythmias, fibrillation arrhythmias, cardiacsynchronization arrhythmias and/or to produce any other suitableelectrical stimulation therapy. Some more common electrical stimulationtherapies include anti-tachycardia pacing (ATP) therapy, cardiacresynchronization therapy (CRT), and cardioversion/defibrillationtherapy. In some cases, the pulse generator 104 may provide acontrollable pulse energy. In some cases, the pulse generator 104 mayallow the controller to control the pulse voltage, pulse width, pulseshape or morphology, and/or any other suitable pulse characteristic.

In some examples, the LCP 100 may include an electrical sensing module106, and in some cases, a mechanical sensing module 108. The electricalsensing module 106 may be configured to sense the cardiac electricalactivity of the heart. For example, the electrical sensing module 106may be connected to the electrodes 114/114′, and the electrical sensingmodule 106 may be configured to receive cardiac electrical signalsconducted through the electrodes 114/114′. The cardiac electricalsignals may represent local information from the chamber in which theLCP 100 is implanted. For instance, if the LCP 100 is implanted within aventricle of the heart (e.g. RV, LV), cardiac electrical signals sensedby the LCP 100 through the electrodes 114/114′ may represent ventricularcardiac electrical signals. In some cases, the LCP 100 may be configuredto detect cardiac electrical signals from other chambers (e.g. farfield), such as the P-wave from the atrium.

The mechanical sensing module 108 may include one or more sensors, suchas an accelerometer, a pressure sensor, a heart sound sensor, ablood-oxygen sensor, a chemical sensor, a temperature sensor, a flowsensor and/or any other suitable sensors that are configured to measureone or more mechanical/chemical parameters of the patient. Both theelectrical sensing module 106 and the mechanical sensing module 108 maybe connected to a processing module 110, which may provide signalsrepresentative of the sensed mechanical parameters. Although describedwith respect to FIG. 1 as separate sensing modules, in some cases, theelectrical sensing module 106 and the mechanical sensing module 108 maybe combined into a single sensing module, as desired.

The electrodes 114/114′ can be secured relative to the housing 120 butexposed to the tissue and/or blood surrounding the LCP 100. In somecases, the electrodes 114 may be generally disposed on either end of theLCP 100 and may be in electrical communication with one or more of themodules 102, 104, 106, 108, and 110. The electrodes 114/114′ may besupported by the housing 120, although in some examples, the electrodes114/114′ may be connected to the housing 120 through short connectingwires such that the electrodes 114/114′ are not directly securedrelative to the housing 120. In examples where the LCP 100 includes oneor more electrodes 114′, the electrodes 114′ may in some cases bedisposed on the sides of the LCP 100, which may increase the number ofelectrodes by which the LCP 100 may sense cardiac electrical activity,deliver electrical stimulation and/or communicate with an externalmedical device. The electrodes 114/114′ can be made up of one or morebiocompatible conductive materials such as various metals or alloys thatare known to be safe for implantation within a human body. In someinstances, the electrodes 114/114′ connected to the LCP 100 may have aninsulative portion that electrically isolates the electrodes 114/114′from adjacent electrodes, the housing 120, and/or other parts of the LCP100. In some cases, one or more of the electrodes 114/114′ may beprovided on a tail (not shown) that extends away from the housing 120.

The processing module 110 can be configured to control the operation ofthe LCP 100. For example, the processing module 110 may be configured toreceive electrical signals from the electrical sensing module 106 and/orthe mechanical sensing module 108. Based on the received signals, theprocessing module 110 may determine, for example, abnormalities in theoperation of the heart H. Based on any determined abnormalities, theprocessing module 110 may control the pulse generator module 104 togenerate and deliver electrical stimulation in accordance with one ormore therapies to treat the determined abnormalities. The processingmodule 110 may further receive information from the communication module102. In some examples, the processing module 110 may use such receivedinformation to help determine whether an abnormality is occurring,determine a type of abnormality, and/or to take particular action inresponse to the information. The processing module 110 may additionallycontrol the communication module 102 to send/receive information to/fromother devices.

In some examples, the processing module 110 may include a pre-programmedchip, such as a very-large-scale integration (VLSI) chip and/or anapplication specific integrated circuit (ASIC). In such embodiments, thechip may be pre-programmed with control logic in order to control theoperation of the LCP 100. By using a pre-programmed chip, the processingmodule 110 may use less power than other programmable circuits (e.g.general purpose programmable microprocessors) while still being able tomaintain basic functionality, thereby potentially increasing the batterylife of the LCP 100. In other examples, the processing module 110 mayinclude a programmable microprocessor. Such a programmablemicroprocessor may allow a user to modify the control logic of the LCP100 even after implantation, thereby allowing for greater flexibility ofthe LCP 100 than when using a pre-programmed ASIC. In some examples, theprocessing module 110 may further include a memory, and the processingmodule 110 may store information on and read information from thememory. In other examples, the LCP 100 may include a separate memory(not shown) that is in communication with the processing module 110,such that the processing module 110 may read and write information toand from the separate memory.

The battery 112 may provide power to the LCP 100 for its operations.Because the LCP 100 is an implantable device, access to the LCP 100 maybe limited after implantation. Accordingly, it is desirable to havesufficient battery capacity to deliver therapy over a period oftreatment such as days, weeks, months, years or even decades. In someinstances, the battery 112 may a rechargeable battery, which may helpincrease the useable lifespan of the LCP 100. In other examples, thebattery 112 may be some other type of power source, as desired. In somecases, the battery 112 may not be battery at all, but rather may besuper capacitor or other charge storage device. In some cases, the LCP100 may include a receiver coil for receiving near-field energy.Charging circuitry may be operatively coupled with the receiving coiland the battery 112, and may be configured to use the non-radiativenear-field energy received via the receiving coil to charge the battery112.

To implant the LCP 100 inside a patient's body, an operator (e.g., aphysician, clinician, etc.), may fix the LCP 100 to the cardiac tissueof the patient's heart. To facilitate fixation, the LCP 100 may includeone or more anchors 116. The anchor 116 may include any one of a numberof fixation or anchoring mechanisms. For example, the anchor 116 mayinclude one or more pins, staples, threads, screws, helix, tines, and/orthe like. In some examples, although not shown, the anchor 116 mayinclude threads on its external surface that may run along at least apartial length of the anchor 116. The threads may provide frictionbetween the cardiac tissue and the anchor to help fix the anchor 116within the cardiac tissue. In other examples, the anchor 116 may includeother structures such as barbs, spikes, or the like to facilitateengagement with the surrounding cardiac tissue.

FIG. 2 depicts an example of another or second medical device (MD) 200,which may be used in conjunction with the LCP 100 (FIG. 1) in order todetect and/or treat cardiac abnormalities. In some cases, the MD 200 maybe considered as an example of the IMD and/or the LCP. In the exampleshown, the MD 200 may include a communication module 202, a pulsegenerator module 204, an electrical sensing module 206, a mechanicalsensing module 208, a processing module 210, and a battery 218. Each ofthese modules may be similar to the modules 102, 104, 106, 108, and 110of LCP 100. Additionally, the battery 218 may be similar to the battery112 of the LCP 100. In some examples, however, the MD 200 may have alarger volume within the housing 220. In such examples, the MD 200 mayinclude a larger battery and/or a larger processing module 210 capableof handling more complex operations than the processing module 110 ofthe LCP 100.

While it is contemplated that the MD 200 may be another leadless devicesuch as shown in FIG. 1, in some instances the MD 200 may include leadssuch as leads 212. The leads 212 may include electrical wires thatconduct electrical signals between the electrodes 214 and one or moremodules located within the housing 220. In some cases, the leads 212 maybe connected to and extend away from the housing 220 of the MD 200. Insome examples, the leads 212 are implanted on, within, or adjacent to aheart of a patient. The leads 212 may contain one or more electrodes 214positioned at various locations on the leads 212, and in some cases atvarious distances from the housing 220. Some leads 212 may only includea single electrode 214, while other leads 212 may include multipleelectrodes 214. Generally, the electrodes 214 are positioned on theleads 212 such that when the leads 212 are implanted within the patient,one or more of the electrodes 214 are positioned to perform a desiredfunction. In some cases, the one or more of the electrodes 214 may be incontact with the patient's cardiac tissue. In some cases, the one ormore of the electrodes 214 may be positioned subcutaneously and outsideof the patient's heart. In some cases, the electrodes 214 may conductintrinsically generated electrical signals to the leads 212, e.g.signals representative of intrinsic cardiac electrical activity. Theleads 212 may, in turn, conduct the received electrical signals to oneor more of the modules 202, 204, 206, and 208 of the MD 200. In somecases, the MD 200 may generate electrical stimulation signals, and theleads 212 may conduct the generated electrical stimulation signals tothe electrodes 214. The electrodes 214 may then conduct the electricalsignals and delivery the signals to the patient's heart (either directlyor indirectly).

The mechanical sensing module 208, as with the mechanical sensing module108, may contain or be electrically connected to one or more sensors,such as accelerometers, acoustic sensors, blood pressure sensors, heartsound sensors, blood-oxygen sensors, and/or other sensors which areconfigured to measure one or more mechanical/chemical parameters of theheart and/or patient. In some examples, one or more of the sensors maybe located on the leads 212, but this is not required. In some examples,one or more of the sensors may be located in the housing 220.

While not required, in some examples, the MD 200 may be an implantablemedical device. In such examples, the housing 220 of the MD 200 may beimplanted in, for example, a transthoracic region of the patient. Thehousing 220 may generally include any of a number of known materialsthat are safe for implantation in a human body and may, when implanted,hermetically seal the various components of the MD 200 from fluids andtissues of the patient's body.

In some cases, the MD 200 may be an implantable cardiac pacemaker (ICP).In this example, the MD 200 may have one or more leads, for example theleads 212, which are implanted on or within the patient's heart. The oneor more leads 212 may include one or more electrodes 214 that are incontact with cardiac tissue and/or blood of the patient's heart. The MD200 may be configured to sense intrinsically generated cardiacelectrical signals and determine, for example, one or more cardiacarrhythmias based on analysis of the sensed signals. The MD 200 may beconfigured to deliver CRT, ATP therapy, bradycardia therapy, and/orother therapy types via the leads 212 implanted within the heart. Insome examples, the MD 200 may additionally be configured providedefibrillation therapy.

In some instances, the MD 200 may be an implantablecardioverter-defibrillator (ICD). In such examples, the MD 200 mayinclude one or more leads implanted within a patient's heart. The MD 200may also be configured to sense cardiac electrical signals, determineoccurrences of tachyarrhythmias based on the sensed signals, and may beconfigured to deliver defibrillation therapy in response to determiningan occurrence of a tachyarrhythmia. In other examples, the MD 200 may bea subcutaneous implantable cardioverter-defibrillator (S-ICD). Inexamples where the MD 200 is an S-ICD, one of the leads 212 may be asubcutaneously implanted lead. In at least some examples where the MD200 is an S-ICD, the MD 200 may include only a single lead which isimplanted subcutaneously, but this is not required. In some instances,the lead(s) may have one or more electrodes that are placedsubcutaneously and outside of the chest cavity. In other examples, thelead(s) may have one or more electrodes that are placed inside of thechest cavity, such as just interior of the sternum but outside of theheart H.

In some examples, the MD 200 may not be an implantable medical device.Rather, the MD 200 may be a device external to the patient's body, andmay include skin-electrodes that are placed on a patient's body. In suchexamples, the MD 200 may be able to sense surface electrical signals(e.g. cardiac electrical signals that are generated by the heart orelectrical signals generated by a device implanted within a patient'sbody and conducted through the body to the skin). In such examples, theMD 200 may be configured to deliver various types of electricalstimulation therapy, including, for example, defibrillation therapy.

In some cases, the MD 200 may be external to the patient's body and mayinclude a transmit coil that is configured to transmit near-field energyto an implanted IMD. The MD 200 may also include an output driver fordriving the transmit coil at a transmit frequency and a transmitamplitude. The transmit frequency and/or transmit amplitude may betuned, sometimes actively tuned, so as to deliver an acceptable transmitpower to a receive coil of the implanted IMD. The transmit power may beused to recharge a power source of the implanted IMD.

FIG. 3 illustrates an example of a medical device system and acommunication pathway through which multiple medical devices 302, 304,306, and/or 310 may communicate. In the example shown, the medicaldevice system 300 may include LCPs 302 and 304, external medical device306, and other sensors/devices 310. The external device 306 may be anyof the devices described previously with respect to the MD 200. Othersensors/devices 310 may also be any of the devices described previouslywith respect to the MD 200. In some instances, other sensors/devices 310may include a sensor, such as an accelerometer, an acoustic sensor, ablood pressure sensor, or the like. In some cases, other sensors/devices310 may include an external programmer device that may be used toprogram one or more devices of the system 300.

Various devices of the system 300 may communicate via communicationpathway 308. For example, the LCPs 302 and/or 304 may sense intrinsiccardiac electrical signals and may communicate such signals to one ormore other devices 302/304, 306, and 310 of the system 300 viacommunication pathway 308. In one example, one or more of the devices302/304 may receive such signals and, based on the received signals,determine an occurrence of an arrhythmia. In some cases, the device ordevices 302/304 may communicate such determinations to one or more otherdevices 306 and 310 of the system 300. In some cases, one or more of thedevices 302/304, 306, and 310 of the system 300 may take action based onthe communicated determination of an arrhythmia, such as by delivering asuitable electrical stimulation to the heart of the patient. It iscontemplated that the communication pathway 308 may communicate using RFsignals, inductive coupling, optical signals, acoustic signals, or anyother signals suitable for communication. Additionally, in at least someexamples, communication pathway 308 may include multiple signal types.For instance, other sensors/device 310 may communicate with the externaldevice 306 using a first signal type (e.g. RF communication) butcommunicate with the LCPs 302/304 using a second signal type (e.g.conducted communication). Further, in some examples, communicationbetween devices may be limited. For instance, as described above, insome examples, the LCPs 302/304 may communicate with the external device306 only through other sensors/devices 310, where the LCPs 302/304 sendsignals to other sensors/devices 310, and other sensors/devices 310relay the received signals to the external device 306.

In some cases, the communication pathway 308 may include conductedcommunication. Accordingly, devices of the system 300 may havecomponents that allow for such conducted communication. For instance,the devices of system 300 may be configured to transmit conductedcommunication signals (e.g. current and/or voltage pulses) into thepatient's body via one or more electrodes of a transmitting device, andmay receive the conducted communication signals (e.g. pulses) via one ormore electrodes of a receiving device. The patient's body may “conduct”the conducted communication signals (e.g. pulses) from the one or moreelectrodes of the transmitting device to the electrodes of the receivingdevice in the system 300. In such examples, the delivered conductedcommunication signals (e.g. pulses) may differ from pacing or othertherapy signals. For example, the devices of the system 300 may deliverelectrical communication pulses at an amplitude/pulse width that issub-capture threshold to the heart. Although, in some cases, theamplitude/pulse width of the delivered electrical communication pulsesmay be above the capture threshold of the heart, but may be deliveredduring a blanking period of the heart (e.g. refractory period) and/ormay be incorporated in or modulated onto a pacing pulse, if desired.

Delivered electrical communication pulses may be modulated in anysuitable manner to encode communicated information. In some cases, thecommunication pulses may be pulse width modulated or amplitudemodulated. Alternatively, or in addition, the time between pulses may bemodulated to encode desired information. In some cases, conductedcommunication pulses may be voltage pulses, current pulses, biphasicvoltage pulses, biphasic current pulses, or any other suitableelectrical pulse as desired. Alternatively, or in addition, thecommunication pathway 308 may include radiofrequency (RF) communication,inductive communication, optical communication, acoustic communicationand/or any other suitable communication, as desired.

FIG. 4 shows an illustrative medical device system. In FIG. 4, an LCP402 is shown fixed to the interior of the left ventricle of the heart410, and a pulse generator 406 is shown coupled to a lead 412 having oneor more electrodes 408 a-408 c. In some cases, the pulse generator 406may be part of a subcutaneous implantable cardioverter-defibrillator(S-ICD), and the one or more electrodes 408 a-408 c may be positionedsubcutaneously. In some cases, the one or more electrodes 408 a-408 cmay be placed inside of the chest cavity but outside of the heart, suchas just interior of the sternum.

In some cases, the LCP 402 may communicate with the subcutaneousimplantable cardioverter-defibrillator (S-ICD). In some cases, the lead412 and/or pulse generator 406 may include an accelerometer 414 thatmay, for example, be configured to sense vibrations that may beindicative of heart sounds.

In some cases, the LCP 402 may be in the right ventricle, right atrium,left ventricle or left atrium of the heart, as desired. In some cases,more than one LCP 402 may be implanted. For example, one LCP may beimplanted in the right ventricle and another may be implanted in theright atrium. In another example, one LCP may be implanted in the rightventricle and another may be implanted in the left ventricle. In yetanother example, one LCP may be implanted in each of the chambers of theheart.

FIG. 5 is a side view of an illustrative implantable leadless cardiacpacemaker (LCP) 610. The LCP 610 may be similar in form and function tothe LCP 100 described above. The LCP 610 may include any of the modulesand/or structural features described above with respect to the LCP 100described above. The LCP 610 may include a shell or housing 612 having aproximal end 614 and a distal end 616. The illustrative LCP 610 includesa first electrode 620 secured relative to the housing 612 and positionedadjacent to the distal end 616 of the housing 612 and a second electrode622 secured relative to the housing 612 and positioned adjacent to theproximal end 614 of the housing 612. In some cases, the housing 612 mayinclude a conductive material and may be insulated along a portion ofits length. A section along the proximal end 614 may be free ofinsulation so as to define the second electrode 622. The electrodes 620,622 may be sensing and/or pacing electrodes to provide electro-therapyand/or sensing capabilities. The first electrode 620 may be capable ofbeing positioned against or may otherwise contact the cardiac tissue ofthe heart while the second electrode 622 may be spaced away from thefirst electrode 620. The first and/or second electrodes 620, 622 may beexposed to the environment outside the housing 612 (e.g. to blood and/ortissue).

In some cases, the LCP 610 may include a pulse generator (e.g.,electrical circuitry) and a power source (e.g., a battery) within thehousing 612 to provide electrical signals to the electrodes 620, 622 tocontrol the pacing/sensing electrodes 620, 622. While not explicitlyshown, the LCP 610 may also include, a communications module, anelectrical sensing module, a mechanical sensing module, and/or aprocessing module, and the associated circuitry, similar in form andfunction to the modules 102, 106, 108, 110 described above. The variousmodules and electrical circuitry may be disposed within the housing 612.Electrical connections between the pulse generator and the electrodes620, 622 may allow electrical stimulation to heart tissue and/or sense aphysiological condition.

In the example shown, the LCP 610 includes a fixation mechanism 624proximate the distal end 616 of the housing 612. The fixation mechanism624 is configured to attach the LCP 610 to a wall of the heart H, orotherwise anchor the LCP 610 to the anatomy of the patient. In someinstances, the fixation mechanism 624 may include one or more, or aplurality of hooks or tines 626 anchored into the cardiac tissue of theheart H to attach the LCP 610 to a tissue wall. In other instances, thefixation mechanism 624 may include one or more, or a plurality ofpassive tines, configured to entangle with trabeculae within the chamberof the heart H and/or a helical fixation anchor configured to be screwedinto a tissue wall to anchor the LCP 610 to the heart H. These are justexamples.

The LCP 610 may further include a docking member 630 proximate theproximal end 614 of the housing 612. The docking member 630 may beconfigured to facilitate delivery and/or retrieval of the LCP 610. Forexample, the docking member 630 may extend from the proximal end 614 ofthe housing 612 along a longitudinal axis of the housing 612. Thedocking member 630 may include a head portion 632 and a neck portion 634extending between the housing 612 and the head portion 632. The headportion 632 may be an enlarged portion relative to the neck portion 634.For example, the head portion 632 may have a radial dimension from thelongitudinal axis of the LCP 610 that is greater than a radial dimensionof the neck portion 634 from the longitudinal axis of the LCP 610. Insome cases, the docking member 630 may further include a tetherretention structure 636 extending from or recessed within the headportion 632. The tether retention structure 636 may define an opening638 configured to receive a tether or other anchoring mechanismtherethrough. While the retention structure 636 is shown as having agenerally “U-shaped” configuration, the retention structure 636 may takeany shape that provides an enclosed perimeter surrounding the opening638 such that a tether may be securably and releasably passed (e.g.looped) through the opening 638. In some cases, the retention structure636 may extend though the head portion 632, along the neck portion 634,and to or into the proximal end 614 of the housing 612. The dockingmember 630 may be configured to facilitate delivery of the LCP 610 tothe intracardiac site and/or retrieval of the LCP 610 from theintracardiac site. While this describes one example docking member 630,it is contemplated that the docking member 630, when provided, can haveany suitable configuration.

It is contemplated that the LCP 610 may include one or more pressuresensors 640 coupled to or formed within the housing 612 such that thepressure sensor(s) is exposed to the environment outside the housing 612to measure blood pressure within the heart. For example, if the LCP 610is placed in the left ventricle, the pressure sensor(s) 640 may measurethe pressure within the left ventricle. If the LCP 610 is placed inanother portion of the heart (such as one of the atriums or the rightventricle), the pressures sensor(s) may measure the pressure within thatportion of the heart. The pressure sensor(s) 640 may include a MEMSdevice, such as a MEMS device with a pressure diaphragm andpiezoresistors on the diaphragm, a piezoelectric sensor, acapacitor-Micro-machined Ultrasonic Transducer (cMUT), a condenser, amicro-monometer, or any other suitable sensor adapted for measuringcardiac pressure. The pressures sensor(s) 640 may be part of amechanical sensing module described herein. It is contemplated that thepressure measurements obtained from the pressures sensor(s) 640 may beused to generate a pressure curve over cardiac cycles. The pressurereadings may be taken in combination with impedance measurements (e.g.the impedance between electrodes 620 and 622) to generate apressure-impedance loop for one or more cardiac cycles as will bedescribed in more detail below. The impedance may be a surrogate forchamber volume, and thus the pressure-impedance loop may berepresentative for a pressure-volume loop for the heart H.

In some embodiments, the LCP 610 may be configured to measure impedancebetween the electrodes 620, 622. More generally, the impedance may bemeasured between other electrode pairs, such as the additionalelectrodes 114′ described above. In some cases, the impedance may bemeasure between two spaced LCP's, such as two LCP's implanted within thesame chamber (e.g. LV) of the heart H, or two LCP's implanted indifferent chambers of the heart H (e.g. RV and LV). The processingmodule of the LCP 610 and/or external support devices may derive ameasure of cardiac volume from intracardiac impedance measurements madebetween the electrodes 620, 622 (or other electrodes). Primarily due tothe difference in the resistivity of blood and the resistivity of thecardiac tissue of the heart H, the impedance measurement may vary duringa cardiac cycle as the volume of blood (and thus the volume of thechamber) surrounding the LCP changes. In some cases, the measure ofcardiac volume may be a relative measure, rather than an actual measure.In some cases, the intracardiac impedance may be correlated to an actualmeasure of cardiac volume via a calibration process, sometimes performedduring implantation of the LCP(s). During the calibration process, theactual cardiac volume may be determined using fluoroscopy or the like,and the measured impedance may be correlated to the actual cardiacvolume.

In some cases, the LCP 610 may be provided with energy deliverycircuitry operatively coupled to the first electrode 620 and the secondelectrode 622 for causing a current to flow between the first electrode620 and the second electrode 622 in order to determine the impedancebetween the two electrodes 620, 622 (or other electrode pair). It iscontemplated that the energy delivery circuitry may also be configuredto deliver pacing pulses via the first and/or second electrodes 620,622. The LCP 610 may further include detection circuitry operativelycoupled to the first electrode 620 and the second electrode 622 fordetecting an electrical signal received between the first electrode 620and the second electrode 622. In some instances, the detection circuitrymay be configured to detect cardiac signals received between the firstelectrode 620 and the second electrode 622.

When the energy delivery circuitry delivers a current between the firstelectrode 620 and the second electrode 622, the detection circuitry maymeasure a resulting voltage between the first electrode 620 and thesecond electrode 622 (or between a third and fourth electrode separatefrom the first electrode 620 and the second electrode 622, not shown) todetermine the impedance. When the energy delivery circuitry delivers avoltage between the first electrode 620 and the second electrode 622,the detection circuitry may measure a resulting current between thefirst electrode 620 and the second electrode 622 (or between a third andfourth electrode separate from the first electrode 620 and the secondelectrode 622) to determine the impedance.

FIG. 6 provides a highly schematic illustration of a patient 700 havingan implantable device (IMD) 702 implanted within the patient 700. Whilethe IMD 702 is shown as being in or near the patient's chest, it will beappreciated that this is merely illustrative, as the IMD 702, dependingon functionality, may be implanted in other locations within the patient700. A transmitter 704 is shown exterior to the patient 700. In somecases, the transmitter 704 may be configured to transmit reactivenear-field energy that is of a wavelength (or frequency, as wavelengthand frequency are related by the numerical speed of light) and amplitudethat can safety pass into the patient 700 to the IMD 702 without causingexcessive tissue heating or other potentially damaging effects to thepatient 700.

The transmitter 704 may take any suitable form. For example, while shownschematically as a box in FIG. 6, the transmitter 704 may be sized andconfigured for the patient 700 to periodically wear about their neck ona lanyard or in a shirt pocket, which would place the transmitter 704proximate their chest, at about the same vertical and horizontalposition as the IMD 702 within the patient's chest. In some cases, thetransmitter 704 may be built into the back of a chair that the patient700 would periodically sit in to recharge the IMD 702. The chair couldbe in the patient's home, for a daily recharge, for example, or could beat a remote location such as a medical clinic, for a patient 700 havinga longer recharge schedule.

As another example, the transmitter 704 could be built into a bed suchthat the transmitter 704 could at least partially recharge the IMD 702each evening when the patient 700 sleeps. In some cases, the transmitter704 could be configured to only transmit once per week, or once permonth, for example, depending on the power requirements of the IMD 702.In some cases, the transmitter 704 and the IMD 702 may communicate witheach other. When so provided, the IMD 702 may report its current batteryrecharge level to the transmitter 704, and if the current batteryrecharge level is below a threshold, the transmitter 704 may transmitpower to the IMD 702.

It will be appreciated that the IMD 702 may be configured toperiodically receive near-field energy at a wavelength and intensitythat is safe for the patient 700 and that the IMD 702 may use torecharge a rechargeable power source within the IMD 702. The near-fieldenergy may be received at a rate that exceeds a rate at which power isbeing drawn from the rechargeable battery and consumed by variouscomponents within the IMD 702.

FIG. 7 provides an illustrative circuit for a coupled inductor system800. Inductive coupling is the near-field wireless transmission ofelectrical energy between a source 802 and a device 804. In some cases,the source 802 may transfer power from a source inductor 806 (e.g.source coil) to a device inductor 808 (e.g. device coil) by a magneticfield. The system 800, therefore, may act as a transformer. In somecases, a signal generator 810 may generate an alternating current (AC)through the source inductor 806 and create an oscillating magneticfield. The signal generator 810 may include an output driver. Themagnetic field may pass through the device inductor 808 and induce analternating electromagnetic force (EMF), which creates an alternatingcurrent (AC) in the device 804. The induced AC may either drive a load812 directly, or be rectified to direct current (DC) by a rectifier (notshown) in the device 804, which drives the load 812.

In some cases, the power transferred may increase with frequency andmutual inductance between the source inductor 806 and the deviceinductor 808, which may depend on their geometry and the distancebetween them. For example, if the source inductor 806 and the deviceinductor 808 are on the same axis (i.e., a primary capture axis) andclose together so the magnetic flux from the source inductor 806 passesthrough the device inductor 808, the transfer of power may approach100%. The greater the separation between the coils, the more themagnetic flux from the source inductor 806 may miss the device inductor808, and the transfer of power may decrease.

In some cases, the source inductor 806 and/or the device inductor 808may be fitted with magnetic cores. A magnetic core can be a piece ofmagnetically active material with a high magnetic permeability used toconfine and guide magnetic fields in electrical, electromechanical andmagnetic devices such as electromagnets, transformers, generators,inductors, and other magnetic assemblies. In some cases, the magneticcore may be made of ferromagnetic metal such as iron, or ferromagneticcompounds such as ferrites. The high permeability, relative to thesurrounding atmosphere, may cause the magnetic field lines to beconcentrated in the ferrite core. In some cases, the use of the ferritecore can concentrate the strength and increase the effect of magneticfields produced by the source inductor 806 and may improve inductivecoupling and the transfer of power.

In some cases, the system may achieve resonant inductive coupling. Inthis case, the source 802 can be tuned to resonant at the same frequencyas the device 804. In some cases, the source 802 can include the sourceinductor 806 connected to a capacitor 814. The resonance between thesource inductor 806 and the device inductor 808 can increase thecoupling and the transmitted power. In some cases, when the system 800achieves resonant inductive coupling, the source 802 and the device 804may interact with each other more strongly than they do withnon-resonant objects and power losses due to absorption in stray nearbyobjects may be reduced.

FIG. 8 provides a cross-sectional view of the illustrative IMD 702. Insome cases, the IMD 702 includes a device housing 706 that may encompassa receiving coil 708, charging circuitry 710, a rechargeable powersource 712, therapeutic circuitry 714, and a controller 717. In variousembodiments, the housing 706 may have a proximal end 716 and a distalend 718. The IMD 702 may include a first electrode 715 positionedadjacent to the distal end 718 of the housing 706 and a second electrode719 positioned adjacent to the proximal end 716 of the housing 706. Insome cases, the housing 706 may include a conductive material and may beinsulated along a portion of its length. A section along the proximalend 716 may be free of insulation so as to define the second electrode719. This is just one example implementation. The electrodes 715, 719may be sensing and/or pacing electrodes to provide electro-therapyand/or sensing capabilities. The first electrode 715 may be capable ofbeing positioned against or may otherwise contact cardiac tissue of aheart while the second electrode 719 may be spaced away from the firstelectrode 715, and thus spaced away from the cardiac tissue.

The illustrative IMD 702 may include a fixation mechanism 720 proximatethe distal end 718 of the housing 706, which may be configured to attachthe IMD 702 to a tissue wall of the heart, or otherwise anchor the IMD702 to the anatomy of the patient. As shown in FIG. 8, in someinstances, the fixation mechanism 720 may include one or more, or aplurality of hooks or tines anchored into the cardiac tissue of theheart to attach the IMD 702 to the tissue wall. In other instances, thefixation mechanism 720 may include one or more, or a plurality ofpassive tines, configured to entangle with trabeculae within the chamberof the heart and/or a helical fixation anchor configured to be screwedinto the tissue wall to anchor the IMD 702 to the heart.

In some cases, the IMD 702 may include a docking member 722 proximatethe proximal end 716 of the housing 706 configured to facilitatedelivery and/or retrieval of the IMD 702. For example, the dockingmember 722 may extend from the proximal end 716 of the housing 706 alonga longitudinal axis of the housing 706. The docking member 722 mayinclude a head portion 724 and a neck portion 726 extending between thehousing 706 and the head portion 724. The head portion 724 may be anenlarged portion relative to the neck portion 726. For example, the headportion 724 may have a radial dimension from the longitudinal axis ofthe IMD 702 which is greater than a radial dimension of the neck portion726 from the longitudinal axis of the IMD 702. The docking member 722may further include a tether retention structure 728 extending from thehead portion 724. The tether retention structure 728 may define anopening 730 configured to receive a tether or other anchoring mechanismtherethrough. While the retention structure 728 is shown as having agenerally “U-shaped” configuration, the retention structure 728 may takeany shape which provides an enclosed perimeter surrounding the opening730 such that a tether may be securably and releasably passed (e.g.looped) through the opening 730. The retention structure 728 may extendthough the head portion 724, along the neck portion 726, and to or intothe proximal end 716 of the housing 706. The docking member 722 may beconfigured to facilitate delivery of the IMD 702 to the intracardiacsite and/or retrieval of the IMD 702 from the intracardiac site. Otherdocking members 722 are contemplated.

According to various embodiments, the housing may also be configured fortrans-catheter deployment. In some cases, this means that the housing706 has overall dimensions that enable the IMD 702 to fit within acatheter or similar device for delivering the IMD 702 via a vascularapproach. In some cases, the housing 706 may have an overall length ofperhaps about 50 millimeters or less, or perhaps about 30 millimeters orless, and/or an overall width of perhaps about 20 millimeters or less,or perhaps about 10 millimeters or less. These are just examples.

In some cases, the receiving coil 708 may be any of a variety ofdifferent types of coils. When considering the electromagnetic regionsaround a transmitting coil/antenna, there are three categories; namely,(1) reactive near-field; (2) radiated near-field and (3) radiatedfar-field. “Inductive” charging systems operate in the reactivenear-field region. In inductive power systems, power is typicallytransferred over short distances by magnetic fields using inductivecoupling between coils of wire, such as receiving coil 708 or byelectric fields using capacitive coupling between electrodes. Inradiative power systems (e.g. radiated near-field and radiatedfar-field), power is typically transmitted by beams of electromagnetic(EM) energy. Radiative power systems can often transport energy forlonger distances, but the ability of a receiving antenna to capturesufficient energy can be challenging, particular for applications wherethe size of the receiving antenna is limited.

In some cases, a transmitter (such as transmitter 704 of FIG. 6) and IMD702 may operate between 10 kHz and 100 MHz within the patient's body.When so provided, the system may operate in the reactive near-field (asan inductive charging system). In some cases, the transmitter 704 maytransmit the near-field energy such that a receiving coil (i.e.,receiving coil 708) may capture the near-field energy and provide it tothe charging circuitry 710. In some cases, the charging circuitry 710may be configured to convert the received near-field energy into a formthat may be used to recharge the rechargeable power source 712. In somecases, the receiving coil 708 may be configured to receive sufficientnear-field energy from a wavelength band of near-field energytransmitted from outside the patient 700 (FIG. 6) to recharge therechargeable power source 712 at a rate faster than the rechargeablepower source 712 is depleted by powering the IMD 702 when the wavelengthband of near-field energy is transmitted at an intensity that does notcause heat damage to the patient 700. In various embodiments, the IMD702 may include a temperature sensor (not shown) that may be configuredto determine if self-heating of the IMD 702 is occurring when therechargeable power source 712 is charging. In some cases, the housing706 of the IMD 702 has a substantially cylindrical profile and thereceiving coil 708 may be conformed to the substantially cylindricalprofile of an inner and/or outer surface of the housing 706. In somecases, there may be two or more coils within or on the IMD 702. Forexample, two or more coils may be placed inside the housing 706. In somecases, there may be three coils oriented orthogonal to one another.

The rechargeable power source 712 may be any type of rechargeablebattery, and may take a three dimensional shape that facilitatesincorporation of the rechargeable battery into the device housing 706.In some cases, the rechargeable power source 712 may not be a battery atall, but instead may be a super capacitor, other charge storage deviceor combination of different types of energy storage devices. As will beappreciated, in some cases the device housing 706 may have a cylindricalor substantially cylindrical shape, in which case the rechargeable powersource 712 having a cylindrical or annular profile, such as a buttonbattery or an elongated (in height) battery having a substantiallycylindrical shape, may be useful. It is recognized that there arepossible tradeoffs in rechargeable battery shape and dimensions relativeto performance, so these issues should be considered in designing therechargeable power source 712 for a particular use. While FIG. 8schematically shows a single rechargeable power source 712, in somecases there may be two, three or more distinct rechargeable powersources 712, each electrically coupled with the charging circuitry 710.For example, in some cases, there may be performance advantages inhaving multiple rechargeable power sources 712. In some instances, theremay be packaging advantages to having multiple (and smaller)rechargeable power sources 712.

In some cases, the rechargeable power source 712 may be configured topower the IMD 702, including the therapeutic circuitry 714. In someinstances, the therapeutic circuitry 714 and the rechargeable powersource 712 may provide electrical signals to the electrodes 715, 719 andthus control the pacing/sensing electrodes 715, 719. In some instances,the therapeutic circuitry 714 may be configured to sense one or moresignals via the electrodes 715, 719 and/or stimulate tissue via theelectrodes 715, 719. As a result, the therapeutic circuitry 714 maypace, stimulate tissue, and/or sense a physiological condition at leastpartly in response to the one or more sensed signals. In some cases, thecharging circuitry 710 and the therapeutic circuitry 714 may be locatedon distinct circuit boards or be manifested within distinct integratedcircuits (ICs). In some cases, the charging circuitry 710 and thetherapeutic circuitry 714, while shown as distinct elements, may becombined within a single IC or on a single circuit board.

While two electrodes 715, 719 are illustrated, it will be appreciatedthat in some instances the IMD 702 may include three, four or moredistinct electrodes. Depending on the intended functionality of the IMD702, as discussed above, the electrodes 715, 719 may be used for sensingand/or pacing the patient's heart. In some instances, for example, theIMD 702 may be a leadless cardiac pacemaker (LCP), an implantablemonitoring device or an implantable sensor. In some cases, theelectrodes 715, 719 may be used for communicating with other implanteddevices and/or with external devices. In some cases, communication withother implanted devices may include conductive communication, but thisis not required.

According to various embodiments, the controller 717 may be configuredto monitor the operation of the IMD 702. For instance, the controller717 may be configured to receive electrical signals from the chargingcircuitry 710. Based on the received signals, the controller 717 maydetect the near-field energy received by the receiving coil 708 andgenerate a message regarding the near-field energy. For example, in somecases, the power transfer efficiency between the IMD 702 and atransmitter (e.g., transmitter 704) may depend on the relativeorientation to one another and/or the distance between them. As such,when a transmit coil from the transmitter 704 is within a range of thereceiving coil 708, a magnetic field may flow through the receiving coil708 allowing the receiving coil 708 to receive the near-field energy.The charging circuitry 710 may use the near-field energy to charge therechargeable power source 712 and send a signal to the controller 717 toindicate that the charging circuitry 710 is attempting to charge therechargeable power source 712.

In some cases, the controller 717 may detect whether the signal meets apredetermined characteristic, condition or criteria. The predeterminedcharacteristic, condition, or criteria may, for example, include apredetermined minimum energy capture rate by the receiving coil 708, apredetermined minimum voltage produced by the receiving coil 708, apredetermined minimum current produced by the receiving coil 708, and/orany other suitable characteristic or condition. In some situations, therate at which the charging circuitry 710 is charging the rechargeablepower source 712 may be less than the rate at which the rechargeablepower source 712 is powering the IMD 702. As a result, the rechargeablepower source 712 is still being depleted, albeit at a lower rate.

In some cases, the controller 717 may use the signal sent from thecharging circuitry 710 (or other signal) to determine that thenear-field energy from the transmitter and captured by the receivingcoil 708 is not strong enough to meet the predetermined characteristic,condition or criteria. The controller 717 may then send a communicationmessage (e.g., a signal) to the transmitter indicating that therechargeable power source 712 is not charging sufficiently, and a user(e.g., the patient 700) may be presented with a notification. In somecases, the controller 717 may send a communication message to anexternal device, such as the patient's mobile phone or other device toalert the patient. In further embodiments, the message could be sent toa database over a network connection.

In some cases, the transmitter may include a user-interface withilluminating devises such as LED's, or audio devices, such as speakersor buzzers, to provide the notification. For example, a “not charging”message may be displayed using a red LED and a “charging” message may bedisplayed using a green LED. In this case, the patient 700 may observethat the red LED has turned on and may then realign the transmitter inresponse. In some cases, such a realignment may change the magnetic fluxthrough the receiving coil 708 and increase the near-field energyreceived by the receiving coil 708. The charging circuitry 710 may thenuse the increased near-field energy to charge the rechargeable powersource 712 and send a signal to the controller 717 to indicate that thecharging circuitry 710 is once again, attempting to charge therechargeable power source 712. In this case, the rate at which thecharging circuitry 710 is charging the rechargeable power source 712 maybe deemed acceptable. The controller 717 may then send a communicationmessage to the transmitter indicating that the rechargeable power source712 is charging. In this case, the “charging” message may be displayedto the patient by the green LED turning on.

As discussed above, in various embodiments, the controller 717 may belocated on a pre-programmed VLSI chip, an ASIC, or on a programmablemicroprocessor. In some examples, regardless of whether the controller717 is located on pre-programmed chip or a programmable microprocessor,the controller 717 may be programmed with logic where the controller 717can send a message to alert the patient 700 about predetermined criteriaor a high-priority condition requiring the patient's attention. Forexample, when the transmit coil from the transmitter 704 is within arange of the receiving coil 708, the magnetic field may flow through thereceiving coil 708 allowing the receiving coil 708 to receive thenear-field energy. The charging circuitry 710 may then use thenear-field energy to charge the rechargeable power source 712. In thisembodiment, the controller 717 may be programmed to detect whether thenear-field energy received is great enough to charge the rechargeablepower source 712. In another embodiment, the controller 717 may beprogrammed to detect whether the near-field energy received is greatenough to charge the rechargeable power source 712 within a certainamount of time. For example, in some cases, the controller 717 may beprogrammed to detect whether the received near-field energy will fullycharge the rechargeable power source 712 in 1 hour. In some cases, thecontroller 717 may be programmed to detect whether the receivednear-field energy will fully charge the rechargeable power source 712 in8 hours. In some cases, the controller 717 may be programmed to detectwhether the received near-field energy will fully charge therechargeable power source 712 in 24 hours. In various embodiments, thecharging of the rechargeable power source 712 or the rate at which therechargeable power source 712 is charging may be predeterminedcharacteristics, conditions or criteria, and the controller 717 may beprogrammed to alert the patient when there is a failure to charge therechargeable power source 712 or a failure to meet the rate of chargingor some other predetermined characteristic, condition or criteria.

Continuing with the current example, if the controller 717 detects thatthe rechargeable power source 712 is not charging or the rechargeablesource 712 will not fully charge within a certain amount of time, thecontroller 717 may be programmed to send a communication message to thetransmitter that turns on a red LED indicating that the rechargeablepower source 712 is not charging adequately. Furthermore, if thecontroller 717 detects that the rechargeable power source 712 ischarging or the rechargeable source 712 will fully charge within acertain amount of time, the controller 717 may be further programmed tosend a communication message to the transmitter that turns on a greenLED indicating that the rechargeable power source 712 is adequatelycharging. In some cases, the controller 717 may send a communicationmessage to an external device, such as the patient's mobile phone. Insome cases, when the transmitter receives a communication message thatindicates the rechargeable power source 712 is not charging, therechargeable source 712 will not fully charge within a certain amount oftime, and/or the power received by the receiving coil 708 does not meetsome other predetermined characteristic, condition or criteria, thetransmitter may increase the transmit power to the transmit coil. Thismay include adjusting the frequency and/or amplitude of the signalprovided to the transmit coil.

FIG. 9 provides an illustrative but non-limiting example of at leastsome of the components within an illustrative near-field energytransmitter 704. As shown, the illustrative near-field energytransmitter 704 may include a transmit coil 12, an output driver 14, amonitor 16, and a controller 18. In certain cases, the transmit coil maybe configured to transmit near-field energy to an IMD (e.g., IMD 702)through inductive coupling. As discussed above, inductive coupling isthe near-field wireless transmission of electrical energy between thetransmitter 704 and the IMD 702. In some cases, the transmitter 704 maytransfer power from the transmit coil 12 to a device inductor (e.g.,receiving coil 708) by a magnetic field. In some cases, a signalgenerator (not shown) may generate an AC through the transmit coil 12and create an oscillating magnetic field. The magnetic field may passthrough the receiving coil 708 and induce an alternating EMF, whichcreates an AC in the IMD 702 to power a load (e.g., rechargeable powersource 712).

In some cases, the transmit coil 12 may be fitted with a ferrite core.The high permeability, relative to the surrounding environment, maycause the magnetic field to be concentrated in the ferrite core. In somecases, the use of the ferrite core can concentrate the strength andincrease the effect of magnetic fields produced by electric currentsthrough the transmit coil 12. The magnetic field may also be confinedand guided, using the ferrite core, and may improve coupling, thus,improving the transfer of power.

In various embodiments, the output driver 14 may be configured to drivethe transmit coil 12 at a given frequency and amplitude. In certainembodiments, the output driver 14 may adjust the frequency and/oramplitude at which the near-field energy is transmitted. In some cases,the near-field energy received may depend on the inductive couplingbetween the transmit coil 12 and the receiving coil 708 and in someinstances, the inductive coupling may depend on the frequency at whichthe transmit coil 12 is driven. As such, the near-field energy, and thusthe power, transmitted by the transmit coil 12 may be larger when thetransmit coil 12 is driven by the output driver 14 at one frequency overanother frequency. In some cases, the closer the frequency at which thetransmit coil 12 is driven is to a resonant frequency, the greater thepower that is transmitted between the transmitter 704 and the IMD 702.At the resonant frequency, the transmit coil 12 and the receiving coil708 may achieve resonant inductive coupling, where the transmitted powermay reach a maximum. In some instances, when the transmit coil 12 andthe receiving coil 708 achieve resonant inductive coupling, thetransmitter 704 and the IMD 702 may interact with each other morestrongly than they do with non-resonant objects, and power losses due toabsorption in stray nearby objects may be reduced.

In some cases, a monitor 16 may be configured to detect a measure of thetransmitted power from the transmit coil 12. The transmitted power maybe dependent on the impedance matching between the transmitter(including the transmit coil) and the receiver of the IMD 702. Theimpedance of the receiver of the IMD 702 may include the input impedanceof the receiving coil 708, the input impedance of the charging circuitry710, and the impedance of the medium between the transmit coil and thereceiving coil 708 (e.g. the patient's body). Since the impedance of thepatient's body may change over time (e.g. with respiration, posture,activity level, etc.), the transmitted power may vary over time. To helpincrease the transmitted power, the transmitter may adjust, sometimesactively adjust, the frequency of the transmitted field to better matchthe impedance of the receiver of the IMD 702 (sometimes including theimpedance of the patient's body therebetween).

In some cases, a controller 18 of the transmitter 704 may be operativelycoupled to output driver 14 and monitor 16. The controller 18 may beconfigured to cause the output driver 14 to adjust the transmitfrequency of the near-field energy across two or more transmitfrequencies, identify the transmit power of the near-field energy ateach of the two or more transmit frequencies using the monitor 16,select the transmit frequency of the two or more transmit frequenciesthat results in a transmit power that has a predeterminedcharacteristic, condition or criteria, and set the transmit frequency ofthe output driver 14 to the selected transmit frequency.

In one example, the transmit coil 12 and the receiving coil 708 mayachieve resonant inductive coupling at a resonant frequency. Theresonant frequency may depend on, for example, the impedances of thetransmit coil 12, the impedance of the receiving coil 708 and theimpedance of the patient's body therebetween. As discussed above, thepower transmitted by the transmit coil 12 may be larger as the transmitfrequency becomes closer to the resonant frequency. The monitor 16 maydetect the power transmitted at two or more different transmitfrequencies, and the controller 18 may use this information to identifya frequency that will deliver sufficient power to the IMD 702. In somecases, the controller 18 may attempt to identify the resonancefrequency. In some cases, the controller 18 may identify a suitablefrequency for each of several detectable conditions, such an inhalationphase of the patient, an exhalation phase of the patient, the posture ofthe patient, the activity level of the patient, and/or any otherdetectable condition. Then, when a particular condition is detected, thecontroller 18 may transmit power at the corresponding identifiedfrequency.

In some cases, the controller 18 may periodically monitor the operationof the transmitter 704 such that the transmitter 704 continues to updatethe suitable frequencies. In some cases, the monitoring may be initiatedaccording to a triggering condition. For example, the controller 18 maydetect a decrease in the power transmitted to the IMD 702 when thetransmitter 704 is being run at a driven frequency. The controller 18may then instruct the output driver 14 to adjust the frequencies to oneor more other frequencies and instruct the monitor 16 to detect thetransmitted powers at each of these frequency. The controller 18 maythen identify the transmitted power values for each of these frequenciesand store the transmitted power values. The controller 18 may thencompare the transmitted power values and determine the frequency thatdelivers the maximum transmitted power to the IMD 702. The controller 18may then set the output driver 14 to drive the transmit coil 12 at thisfrequency.

As discussed herein, power transmission may reach a maximum when thetransmit coil 12 and the receiving coil 708 achieve resonant inductivecoupling. Resonant inductive coupling may occur when the transmit coil12 and the receiving coil 708 are configured to resonant at the samefrequency and the transmit frequency equals the resonant frequency. Insome cases, to configure the transmit coil 12 and the receiving coil 708to resonant at the same or similar frequency, the impedance of thetransmitter 704 may be changed to conform with the impedance of the IMD702 (and in some cases, the patient's body therebetween).

In some instances, the impedance of the IMD 702 (and in some cases, thepatient's body therebetween) may vary over time. For example, during thelifespan of the IMD 702, the internal impedance may change due to theaging of the circuitry of an IMD 702. In another example, the impedancemay be affected by an implantation location of the IMD 702, and as aresult, minor shifts or changes from the implantation location and/ororientation may change the internal impedance of the IMD 702. Inaddition, the location of the transmitter 704 relative to the IMD 702may affect the impedance between the transmitter 704 and the IMD 702(sometimes including the impedance of the patient's body therebetween),which may also affect the resonant frequency and the transmission ofpower. Also, changes in body posture, activity level, respiration andother characteristics of the patient may affect the impedance betweenthe transmitter 704 and the IMD 702. To help compensate for thesechanges, the impedance of the transmitter may be changed over time. Morespecifically, the impedance of the output driver 14 and the transmitcoil 12 may be adjusted to match the impedance of the IMD 702 (702(sometimes including the impedance of the patient's body therebetween).This may help bring their resonance frequencies into alignment.Therefore, in some cases, the controller 18 may be configured toinstruct the output driver 14 to adjust the impedance of the transmitter704 such that the impedance of the output driver 14 and the transmitcoil 12 may conform with the impedance of the IMD 702 and the impedanceof the environment separating the transmitter 704 and the IMD 702 (e.g.the patient's body).

In some cases, the controller 18 may periodically monitor the operationof the transmitter 704 such that the transmitter 704 continues totransmit acceptable power. In some cases, the monitoring may beinitiated according to a triggering condition. For example, the monitor16 may detect a decrease in the power transmitted to the IMD 702. Thecontroller 18 may then instruct the output driver 14 to adjust theimpedance to change the resonance frequency of the transmitter 704 anddrive the transmit coil 12 at the adjusted resonant frequency. Thecontroller 18 may then instruct the monitor 16 to detect the transmittedpower. This may be repeated from time to time.

In some cases, near-field energy transmitter 704 is operating torecharge a single IMD in which case output driver 14 and controller 18are configured to optimally recharge the single IMD and monitor 16indicates the status of the recharge of the single IMD. In other cases,the system may contain 2 or more IMDs, as indicated in FIG. 3, andnear-field energy transmitter 704 operates to recharge the multipleIMDs. In this case, output driver 14 and controller 18 may be configuredto optimally recharge the multiple IMDs and monitor 16 may indicate thestatus of the recharge of the multiple IMDs. In a system with multiplerechargeable IMDs, the transmitter 704 may simultaneously recharge bothIMDs or preferentially recharge one or more IMDs based on the chargestatus of all the IMDs.

FIG. 10 provides another illustrative but non-limiting example of atleast some of the components within the near-field energy transmitter704. The configuration and operation of the near-field energytransmitter 704 and its elements may be similar to the configuration andoperation of the near-field energy transmitter 704 and its elementsdescribed with respect to FIG. 9. In some cases, as seen in FIG. 10, thenear-field energy transmitter 704 may also include a posture sensor 22.As discussed herein, in some cases, the location of the transmitter 704relative to the IMD 702 may affect the impedance between the transmitter704 and the IMD 702 which may also affect the transmission of power.Furthermore, the relative location of the IMD 702 within the patient 700may depend on a posture of the patient 700. In some cases, the posturesensor 22 may be configured to detect the posture of the patient 700 andthe controller 18 may be configured use the detection of the posture andrespond to changes in the posture of the patient 700 to control theoperation of the transmitter 704. For example, when the transmitter 704is placed in the range to charge the IMD 702, the controller 18 mayinstruct the posture sensor 22 to detect the posture of the patient 700,which may be a first position. The controller 18 may then control theoperation of the transmitter 704 to determine, select, and set thetransmit frequency at which the output driver 14 drives the transmitcoil 12 to achieve an acceptable power transmission to the IMD 701. Thecontroller 18 may then associate this transmit frequency with the firstposition.

In some cases, the controller 18 may detect a decrease in the powertransmitted to the IMD 702. In response, the controller 18 may instructthe posture sensor 22 to detect the posture of the patient 700, whichmay now be a second position different from the first position. Thecontroller 18 may then control the operation of the transmitter 704 todetermine, select, and set the transmit frequency at which the outputdriver 14 drives the transmit coil 12 to achieve an acceptable powertransmission to the IMD 701. The controller 18 may then associate thistransmit frequency with the second position.

In some cases, the controller 18 may once again detect a decrease in thepower transmitted to the IMD 702. In response, the controller 18 mayinstruct the posture sensor 22 to detect the posture of the patient 700,which may now be a third position that is different from the firstposition and the second position. The controller 18 may then control theoperation of the transmitter 704 to determine, select, and set thetransmit frequency at which the output driver 14 drives the transmitcoil 12 to achieve an acceptable power transmission to the IMD 701. Thecontroller 18 may then associate this transmit frequency with the thirdposition.

In some cases, at a later time, the controller 18 may monitor theposture of the patient via the posture sensor 22. When the posture ofthe patient 700 is detected to be the first position, the controller 18may automatically switch to the transmit frequency that is associatedwith the first position. When the posture of the patient 700 is detectedto be the second position, the controller 18 may automatically switch tothe transmit frequency that is associated with the second position. Whenthe posture of the patient 700 is detected to be the third position, thecontroller 18 may automatically switch to the transmit frequency that isassociated with the third position.

A similar approach may be used in conjunction with a respiration sensor,an activity level sensor and/or any other suitable sensor. For example,with respect to a respiration sensor, the controller 18 may associate afirst transmit frequency with an inhalation phase of the respirationcycle and a second transmit frequency with an exhalation phase of therespiration cycle. Then, when the respiration sensor detects aninhalation phase of the respiration cycle, the controller 18 mayautomatically switch to the first transmit frequency, and when therespiration sensor detects an exhalation phase of the respiration cycle,the controller 18 may automatically switch to the second transmitfrequency.

FIG. 11 provides another illustrative but non-limiting example of atleast some of the components within the near-field energy transmitter704. The configuration and operation of the transmitter 704 and itselements may be similar to the configuration and operation of thetransmitter 704 and its elements described with respect to FIG. 9.Furthermore, in some instances, the transmitter 704 may include theposture sensor 22 similar to the posture sensor 22 described withrespect to FIG. 10. In some cases, as seen in FIG. 11, the transmitter704 may include a communication block 26. The communication block 26 maybe configured to communicate with devices such as sensors, other medicaldevices such as the IMD 702, and/or the like, that are locatedexternally to the transmitter 704. Such devices may be located eitherexternal or internal to the patient's 700 body. Irrespective of thelocation, external devices (i.e. external to the transmitter 704 but notnecessarily external to the patient's 700 body) can communicate with thetransmitter 704 via communication block 26 to accomplish one or moredesired functions. The communication block 26 may be configured to useone or more methods for communicating with the IMD 702. For example, thecommunication block 26 may communicate via radiofrequency (RF) signals,inductive coupling, optical signals, acoustic signals, conductedcommunication signals, and/or any other signals suitable forcommunication. In some cases, the transmitter 704 may communicateinformation, such as sensed electrical signals, data, instructions,messages, R-wave detection markers, etc., to the IMD 702 through thecommunication block 26. The transmitter 702 may additionally receiveinformation such as signals, data, instructions and/or messages from theIMD 702 through the communication block 26, and the transmitter 704 mayuse the received signals, data, instructions and/or messages to performvarious functions, such as charging the rechargeable power source 712,storing received data, and/or performing any other suitable function. Insome cases, the communication block 26 may be used to enablecommunication between the transmitter 704 and the IMD 702 using thenear-field energy. Near-Field communication is a wireless form of shortrange communication using near field magnetic flux for datatransmission.

In certain instances, the communication block 26 may receive messages orinformation from the IMD 702 regarding the power transmitted from thenear-field energy produced by the transmit coil 12. For example, whenthe patient 700 wants to charge the IMD 702, they may bring thetransmitter 704 close to where the IMD 702 is located. In some cases,the communication block 26 may look for or poll for the nearby IMD 702using the near-field energy. The IMD 702 may listen and respond bysending a signal back to the communication block 26 when the transmitter704 is close enough. The communication block 26 may then decipher thesignal and may send a signal to the controller 18 that the IMD 702 iswithin range and the controller 18 may begin the charging process. Thecontroller 18 may then attempt to charge the rechargeable power source712 by instructing the output driver 14 to drive the transmit coil 12such that the near-field energy is transmitted at a first transmitfrequency and/or amplitude. The communication block 26 may then receivea message from the IMD 702 regarding whether the transmitted power meetspredetermined characteristic, condition or criteria. The communicationblock 26 may then send the message to the controller 18. In someinstances, the controller 18 may perform a function or functions basedon whether the transmitted power meets the predetermined characteristic,condition or criteria. For example, the strength of the transmittedpower to the IMD 702 may not be enough to charge the rechargeable powersource 712. As a result, the IMD 702 may send a message to thecommunication block 26 indicating that the transmitted power does notmeet predetermined “charging” criteria. The communication block 26 ofthe transmitter 704 may then send the signal to the controller 18.Additionally or alternatively, in some cases, the communication block 26may send a communication message to an external device, such as thepatient's mobile phone. The controller 18 may then, for example,illuminate a red LED on a user-interface of the transmitter 704 toinform the patient 700 that the IMD 702 is not charging properly. Insome cases, the patient may adjust the position of the transmitter 704in an attempt to better align the transmitter 704 with the IMD 702.Alternatively, or in addition, the controller 18 may adjust the transmitfrequency and/or transmit amplitude of the output driver 14 and thus thetransmit coil 12 in an attempt to increase the transmitted power to theIMD 702. If the transmitted power is deemed sufficient, the IMD 702 maysend a signal to the communication block 26 of the transmitter 704indicating that the transmitted power meets the “charging” criteria. Thecommunication block 26 may then send the signal to the controller 18.Additionally or alternatively, in some cases, the communication block 26may send a communication message to the patient's mobile phone. In somecases, the controller may illuminate a green LED on the user-interfaceof the transmitter 704 to inform the patient 700 that the IMD 702 is nowproperly charging.

FIG. 12 provides another illustrative but non-limiting example of atleast some of the components within the near-field energy transmitter704. The configuration and operation of the transmitter 704 and itselements may be similar to the configuration and operation of thetransmitter 704 and its elements described with respect to FIG. 9 andthe transmitter 704 and its elements described with respect to FIG. 11.For example, when the patient 700 wants to charge the IMD 702, they maybring the transmitter 704 close to where the IMD 702 is located. In somecases, the communication block 26 may look for or poll for the nearbyIMD 702 using the near-field energy. The IMD 702 may listen and respondby sending a signal back to the communication block 26 when thetransmitter 704 is close enough. The communication block 26 may thendecipher the signal and may send a signal to the controller 18 of thetransmitter 704 that the IMD 702 is within range and the controller 18may begin the charging process.

In some cases, the controller 18 may attempt to charge the rechargeablepower source 712 by instructing the output driver 14 to drive thetransmit coil 12 such that the near-field energy is transmitted at atransmit frequency and at a transmit amplitude. The communication block26 may receive a message from the IMD 702 regarding whether thetransmitted power meets one or more predetermined characteristics,conditions or criteria. The communication block 26 may forward themessage to the controller 18. In some instances, the controller 18 mayperform a function or functions based on whether the transmitted powermeets the one or more predetermined characteristics, conditions orcriteria.

In one example, the patient 700 may want to charge the IMD 702 within 1hour. In such a case, a predetermined criteria may be whether the rateat which the rechargeable power source 712 is charging is great enoughto fully charge the rechargeable power source 712 within 1 hour. In somecases, this rate may the rate needed to charge the rechargeable powersource 712 from a completely discharged state to a fully charged state,or it may be the rate needed to charge the rechargeable power source 712from the currently charged state (e.g. half charged) to a fully chargedstate (e.g. from half charged to fully charged). If the transmittedpower to the IMD 702 is not sufficient to charge the rechargeable powersource 712, the IMD 702 may send a message to the communication block 26of the transmitter 704 indicating that the transmitted power (powerreceived at the IMD 702) does not meet a “charging” criteria. Thecommunication block 26 may forward the message to the controller 18. Thecontroller 18 may illuminate a red LED on a user-interface of thetransmitter 704 to inform the patient 700 that the IMD 702 is notcharging. In some cases, the patient may adjust the position of thetransmitter 704 in an attempt to better align the transmitter 704 withthe IMD 702. Alternatively, or in addition, the controller 18 may adjustthe transmit frequency and/or transmit amplitude, and instruct theoutput driver 14 to drive the transmit coil 12 at the adjusted transmitfrequency and/or transmit amplitude. This time, the transmitted power tothe IMD 702 may be sufficient to charge the rechargeable power source712 but not within one hour. As a result, the IMD 702 may send a messageto the communication block 26 indicating that the transmitted powerstill does not meet the “rate of charging” criteria. The communicationblock 26 may then send the message to the controller 18. In some cases,the controller 18 may illuminate a yellow LED on the user-interface ofthe transmitter 704 to show that the IMD 702 is charging, but not fastenough to be fully charged within 1 hour. In some cases, the patient mayagain adjust the position of the transmitter 704 in an attempt to betteralign the transmitter 704 with the IMD 702. Alternatively, or inaddition, the controller 18 may adjust the transmit frequency and/ortransmit amplitude, and instruct the output driver 14 to drive thetransmit coil 12 at the adjusted transmit frequency and/or transmitamplitude. This time, the transmitted power to the IMD 702 may besufficient to charge the rechargeable power source 712 within one hour.As a result, the IMD 702 may send a message to the communication block26 indicating that the transmitted power meets the “rate of charging”criteria. The communication block 26 may then forward the message to thecontroller 18. In some cases, the controller 18 may illuminate a greenLED on the user-interface of the transmitter 704 to show that the IMD702 is charging at a rate that is fast enough to fully charge therechargeable power source 712 within 1 hour. This is just one example.

FIG. 13A provides a schematic side-view and FIG. 13B provides afront-plan view of an illustration of a coil configuration 900 for anear-field transmitter (such as transmitter 704 of FIG. 9) containingmultiple transmit coils 902 a-902 d. Each of the coils 902 a-902 d canbe independently driven by output driver 906 to create near-fieldmagnetic fields 904 a-904 d. Magnetic fields 904 a-904 d form compositemagnetic field 910. Controller 908 may adjust the currents in coils 902a-902 d thereby shifting the spatial peak (i.e. the transmit vector) ofthe composite magnetic field 910 to increase the power delivered to IMD702. Adjusting the spatial peak of the composite magnetic field 910 mayincrease the power delivered to IMD 702 without the need for the patientto move transmitter 704.

FIG. 14A provides an illustrative but non-limiting example of a flexiblesubstrate 30 that may house the transmit coil 12. The configuration andoperation of the transmit coil 12 may be similar to the configurationand operation of the transmit coil 12 described with respect to FIGS.9-12 when used in conjunction with the other elements included in thetransmitter 704 described with respect to FIGS. 9-12.

In some cases, the substrate 30 may be formed of a flat woven fabricthat defines a pocket 38. In some embodiments, the pocket 38 may includea flexible flap-like closure (not shown) which may be folded over thepocket 38 to contain the transmit coil 12 therein. According to variousembodiments, the transmit coil 12 may be configured with low-resistivewindings and an air-core front end. Furthermore, in some cases, thetransmit coil 12 may be composed of a Litz wire and the spacing of thewindings of the transmit coil 12 may be determined to potentially managethe thermal heating relating to the transmit coil 12.

In certain embodiments, the substrate 30 may be composed of one or moretypes of material that is commercially available and characterized byits flexibility and its ability to fit snuggly and/or comfortably to apiece of furniture (e.g., chair 48, from FIG. 14B) or a patient (e.g.,patient 700, from FIG. 14C). Additionally, and in some cases, thesubstrate 30 may include target fiducials 32 sewn, printed, or paintedon the surface of the substrate 30. In various embodiments, the targetfiducials 32 may be used by the patient to assist the patient inaligning the transmit coil 12 with an IMD (e.g., IMD 702) within apatient (e.g., patient 700, from FIG. 14C).

In some cases, the substrate 30 may also be provided with supports forsupporting the pocket 38 at various positions on the patient 700 (fromFIG. 14C) or on a piece of furniture, such as the chair 48 (from FIG.14B), a bed, a couch, etc. By way of example, the substrate 30 mayinclude opposed elongated flexible fabric strap members 34 a, 34 b whichare secured to the substrate 30 and extend normal to the opposed sideedges 40 a, 40 b, respectively. The straps 34 a, 34 b may be formed of asuitable woven polyester fabric, for example. The distal ends of thestraps 34 a, 34 b may be attached to connector members 42 a, 42 b thatmay take many forms, such as hooks, Velcro, screws, pins, clasps,buckles or another type of fastener that may secure connector members 42a, 42 b to one another, respectively, after the position of the straps34 a, 34 b are adjusted to properly secure the substrate 30 in apreferred position on the back of the chair 48, as shown in FIG. 14B, oron the patient's body 700, as shown in FIG. 14C.

In various embodiments, the substrate 30 may include a ferromagneticshield (not shown). In certain configurations, the ferromagnetic shieldmay be located on a side of the transmit coil 12 that is opposite orfaces away from the IMD 702. Such a ferromagnetic shield may help director focus the electromagnetic energy toward the IMD 702.

In some instances, the effectiveness of the ferromagnetic shield maydepend on the material used, its thickness, the size of the shieldedvolume and the frequency of the fields of interest and the size, shapeand orientation of apertures in a shield to an incident electromagneticfield. In some cases, the material used may include sheet metal, a metalscreen, or metal foam. In some cases, the substrate 30 may be coatedwith metallic ink or similar material. The ink may include a carriermaterial loaded with a suitable metal, typically copper or nickel, inthe form of very small particulates. It may be sprayed on the pocket 38and, once dry, may produce a continuous conductive layer of metal. Theseare just examples.

In some cases, the ferromagnetic shield may be made of high magneticpermeability metal alloys, such as sheets of Permalloy and Mu-Metal, orwith nanocrystalline grain structure ferromagnetic metal coatings. Thesematerials may draw a stray magnetic field into themselves and provide apath for the magnetic field around the shielded volume. Theeffectiveness of this type of shielding may depend on the shield'spermeability, which may drop off at low magnetic field strengths and athigh field strengths where the shield becomes saturated. As a result, toachieve low residual fields, the ferromagnetic shield may includeseveral enclosures, one inside the other, each of which successively mayreduce the stray fields.

In various cases, active shielding may be used by creating a field withelectromagnets to cancel the ambient field within the volume outside ofthe body. Solenoids and Helmholtz coils are types of coils that can beused for this purpose. Additionally, superconducting materials can expelmagnetic fields via the Meissner effect.

In some cases, the flexible substrate 30 may include a user-interface 50with illuminating devises such as LED's 52, or audio devices, such asspeakers 54, to display or issue a human perceptible alert if thetransmit coil 12 is deemed to be misaligned with the IMD 702. Forexample, in some cases, misalignment of the transmit coil 12 with theIMD 702 may cause the IMD 702 to not charge sufficiently when thenear-field energy is applied and charging is expected. As a result, theLED 52 may be illuminated and/or the speakers 54 may release a “buzz”sound. The patient 700 may observe the illumination of the LED 52 and/orhear the “buzz” from the speakers 54 and realign the transmit coil 12until the LED 52 is no longer illuminated and/or the speakers 54 stopreleasing the “buzz” sound.

Referring now to FIG. 14B, the substrate 30 may also be configured as anelongated pad or pillow-like member with the transmit coil 12 disposedin the pocket 38 in the manner described above. In certain embodiments,there may be several transmit coils disposed in the pocket 38 topotentially increase the power transmission and decrease the chargingtime of the IMD 702. In some cases, a transmit coil may be selected fromthe transmit coils that offers the most efficient power transmission andpotentially, the least amount of charging time for the IMD 702. Sincethe substrate 30 may be substantially flexible, the substrate 30 may beattached to a chair 48 and used as a lumbar pillow or as a neck orshoulder support while the transmit coil 12 applies the near-fieldenergy, for example. In some cases, the substrate 30 may be attached tothe chair 48 by wrapping the straps 34 a, 34 b around the chair 48 andattaching the connector members 42 a, 42 b to one another. Furthermore,to assist in aligning the transmit coil 12 with the IMD 702, targetfiducials 32 may be used to show the patient where the patient 700should position their torso relative to the transmit coil 12. As aresult, the inductive coupling between the transmit coil 12 and areceiving coil of the IMD 702 may be enhanced and help increase thepower transmission of the near-field energy.

Referring now to FIG. 14C, there is illustrated an illustrative positionin which the substrate 30 may be worn by the patient 700. In some cases,because of the flexibility, the substrate 30 may conform to the contourof the body of the patient 700 to minimize discomfort and help thepatient 700 don conventional outer garments which may not interfere withthe substrate 30 or vice versa. In certain embodiments, a garment wornby the patient 700 may be the flexible substrate 30, and the transmitcoil 12 may be located in or on the garment (e.g., in the pocket of ashirt). In some cases, the substrate 30 may be attached to the patient700 by wrapping the straps 34 a, 34 b around the torso of the patient700 and attaching the connector members 42 a, 42 b to one another.Furthermore, to assist in aligning the transmit coil 12 with the IMD702, target fiducials 32 may be used to show the patient where thepatient 700 should position the pocket 38 relative to a body part (e.g.,the chest). As a result, the inductive coupling between the transmitcoil 12 and the receiving coil of the IMD 702 may be enhanced and helpincrease the power transmission of the near-field energy.

FIG. 15A provides an illustrative but non-limiting example of anotherflexible substrate 40 that may house the transmit coil 12 and anothertransmit coil 42. The configuration and operation of the transmit coils12, 42 may be similar to the configuration and operation of the transmitcoil 12 described with respect to FIGS. 14A-14C. Furthermore, theoperation and configuration of the flexible substrate 40 may be similarto the flexible substrate 30 as described with respect to FIGS. 14A-14C.In some cases, the user-interface 50 may be used to display or issue ahuman perceptible alert if the transmit coil 12 and/or the transmit coil42 are deemed to be misaligned with the IMD 702.

Referring now to FIG. 15B, there is illustrated one position in whichthe substrate 40 of FIG. 15A may be worn by the patient 700. In somecases, because of the flexibility, the substrate 40 may wrap around thepatient's 700 torso and conform to the contour of the body of thepatient 700 to minimize discomfort and enable the patient 700 to donconventional outer garments which may not interfere with the substrate40 or vice versa. In certain embodiments, the transmit coil 12 may beconfigured to be located on a front part 56 of the patient 700 and thetransmit coil 42 may be configured to be located on a back part 58 ofthe patient 700. However, in other embodiments, one or more of thetransmit coils 12, 42 may be configured to be located on another part ofthe patient 700, such as a side part 60. In some cases, the positioningof the transmit coil 12 relative to the transmit coil 42 may provide anincrease in the focusing, steering, guiding, shaping, or confining ofthe near-field energy toward the IMD 702. In some cases, the transmitcoil 42 may be used as an electromagnetic shield for the transmit coil12 by creating a field to cancel, absorb, or minimize the ambient orstray fields or eddy-currents. In various embodiments, the transmit coil12 and transmit coil 42 may communicate with one another, by way offeedback for example, to determine the alignment between the transmitcoil 12 and the transmit 42. In addition, in some cases, theuser-interface 50 may be configured to receive the feedback and use theLED 52 and/or speakers 54 to display or issue a human perceptible alertif the transmit coil 12 is deemed to be misaligned with the transmitcoil 42.

It should be understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of steps without exceeding the scope of thedisclosure. This may include, to the extent that it is appropriate, theuse of any of the features of one example embodiment being used in otherembodiments.

What is claimed is:
 1. A near-field energy transmitter for charging animplantable medical device (IMD), the transmitter comprising: a transmitcoil configured to transmit near-field energy to the IMD; an outputdriver for driving the transmit coil so that the transmit coil transmitsthe near-field energy at a transmit frequency, wherein the transmitfrequency is adjustable; a monitor operatively coupled to the outputdriver for detecting a transmit power of the transmitted near-fieldenergy; a controller operatively coupled to the output driver and themonitor, the controller configured to: cause the output driver to adjustthe transmit frequency of the near-field energy across two or moretransmit frequencies; identify the transmit power of the near-fieldenergy at each of the two or more transmit frequencies using themonitor; select the transmit frequency of the two or more transmitfrequencies that results in a transmit power that has a predeterminedcharacteristic, wherein the predetermined characteristic is that thetransmit power is the maximum transmit power identified for the two ormore transmit frequencies; and set the transmit frequency of the outputdriver to the selected transmit frequency.
 2. The near-field energytransmitter of claim 1, wherein at least one of the transmit frequenciesis a resonant frequency of the output driver and transmit coil, and theoutput driver comprises an adjustable impedance that is adjustable toproduce the resonance frequency.
 3. The near-field energy transmitter ofclaim 1, wherein the controller is configured to detect a decrease inthe transmit power at the selected transmit frequency, and in response:cause the output driver to adjust the transmit frequency of thenear-field energy across two or more transmit frequencies; identify thetransmit power of the near-field energy at each of the two or moretransmit frequencies; select the transmit frequency of the two or moretransmit frequencies that results in a transmit power that has apredetermined characteristic; and set the transmit frequency of theoutput driver to the selected transmit frequency.
 4. The near-fieldenergy transmitter of claim 1, wherein the controller is configured torepeat from time to time the following: cause the output driver toadjust the transmit frequency of the near-field energy across two ormore transmit frequencies; identify the transmit power of the near-fieldenergy at each of the two or more transmit frequencies; select thetransmit frequency of the two or more transmit frequencies that resultsin a transmit power that has a predetermined characteristic; and set thetransmit frequency of the output driver to the selected transmitfrequency.
 5. The near-field energy transmitter of claim 1, furthercomprising a posture sensor for detecting a posture of a patient inwhich the IMD is implanted, and wherein the controller is configured toidentify a transmit frequency for each of two or more postures by: usingthe posture sensor to detect when the patient is in one of the two ormore postures, and when in the detected posture: cause the output driverto adjust the transmit frequency of the near-field energy across two ormore transmit frequencies; identify the transmit power of the near-fieldenergy at each of the two or more transmit frequencies using themonitor; select the transmit frequency of the two or more transmitfrequencies that results in a transmit power that has a predeterminedcharacteristic; and associate the detected posture with the selectedtransmit frequency.
 6. The near-field energy transmitter of claim 5,wherein the controller is further configured to subsequently detect whenthe patient is in one of the two or more postures, and in response, setthe transmit frequency of the output driver to the transmit frequencythat is associated with the detected posture.
 7. The near-field energytransmitter of claim 1, further comprising a communication block forcommunicating with the IMD, and wherein the communication block isconfigured to receive one or more messages from the IMD regarding thetransmit power that is received by the IMD.
 8. The near-field energytransmitter of claim 7, wherein: the output driver is configured todrive the transmit coil so that the transmit coil transmits thenear-field energy at a transmit amplitude, wherein the transmitamplitude is adjustable; and the controller is configured to adjust thetransmit amplitude of the near-field energy so that the transmit powerthat is received by the IMD meets a predetermined criteria.
 9. Thenear-field energy transmitter of claim 8, wherein the one or moremessages received from the IMD indicate whether the transmit power thatis received by the IMD meets the predetermined criteria.
 10. Thenear-field energy transmitter of claim 8, wherein the one or moremessages received from the IMD indicate whether the transmit power thatis received by the IMD does not meet the predetermined criteria.
 11. Thenear-field energy transmitter of claim 1, further comprising a flexiblesubstrate configured to conform to a patient and house the transmittercoil.
 12. The near-field energy transmitter of claim 11, wherein theflexible substrate comprises a strap for securing the flexible substratein place, and wherein the flexible substrate has target fiducials toindicate a torso position of the patient relative to the transmit coil.13. The near-field energy transmitter of claim 11, further comprising aferromagnetic shield along a side of the transmit coil that faces awayfrom the IMD during use.
 14. The near-field energy transmitter of claim11, wherein the flexible substrate is configured to be worn by thepatient.
 15. The near-field energy transmitter of claim 14, furthercomprising a second transmit coil housed by the flexible substrate,wherein the transmit coil is configured to be located on a front of thepatient and the second transmit coil is configured to be located on aside or back of the patient.
 16. The near-field energy transmitter ofclaim 11, wherein the controller is further configured to issue a humanperceptible alert if the transmit coil is deemed to be misaligned withthe 1 MB.
 17. A near-field energy transmitter for charging animplantable medical device (1 MB), the transmitter comprising: atransmit coil configured to transmit near-field energy to the IMD; anoutput driver for driving the transmit coil so that the transmit coiltransmits the near-field energy at a transmit frequency and a transmitamplitude, wherein at least one of the transmit frequency and transmitamplitude is adjustable; a communication block for communicating withthe IMD, wherein the communication block is configured to receive one ormore messages from the IMD regarding the transmit power that is receivedby the IMD; and a controller operatively coupled to the output driverand the communication block, the controller configured to adjust one ormore of the transmit frequency and transmit amplitude of the near-fieldenergy so that the transmit power that is received by the IMD meets apredetermined criteria.
 18. The near-field energy transmitter of claim17, wherein the one or more messages received from the IMD indicate:whether the transmit power that is received by the IMD meets thepredetermined criteria; and/or whether the transmit power that isreceived by the IMD does not meet the predetermined criteria.
 19. Anear-field energy transmitter for charging an implantable medical device(IMD), the transmitter comprising: a transmit coil configured totransmit near-field energy to the IMD; an output driver for driving thetransmit coil so that the transmit coil transmits the near-field energyat a transmit frequency, wherein the transmit frequency is adjustable; amonitor operatively coupled to the output driver for detecting atransmit power of the transmitted near-field energy; a controlleroperatively coupled to the output driver and the monitor, the controllerconfigured to: cause the output driver to adjust the transmit frequencyof the near-field energy across two or more transmit frequencies;identify the transmit power of the near-field energy at each of the twoor more transmit frequencies using the monitor; select the transmitfrequency of the two or more transmit frequencies that results in atransmit power that has a predetermined characteristic; and set thetransmit frequency of the output driver to the selected transmitfrequency; wherein the controller is configured to detect a decrease inthe transmit power at the selected transmit frequency, and in response:cause the output driver to adjust the transmit frequency of thenear-field energy across two or more transmit frequencies; identify thetransmit power of the near-field energy at each of the two or moretransmit frequencies; select the transmit frequency of the two or moretransmit frequencies that results in a transmit power that has apredetermined characteristic; and set the transmit frequency of theoutput driver to the selected transmit frequency.